Ultrasonic fluid speed of sound and flow meter apparatus and method

ABSTRACT

An ultrasonic speed of sound and flow metering system which may utilize only one pair of ultrasonic transducers by incorporating a unique time share feature. In one embodiment a direct synthesis of a frequency proportional to the speed of sound in a flowing medium is obtained using one voltage controlled oscillator. An additional direct synthesis of a data frequency proportional to the flow of the medium is derived from signals inversely proportional to sound energy transit times upstream and downstream.

United States Patent 1191 Brown Dec. 25, 1973 [541 ULTRASONIC FLUIDSPEED or SOUND 5,420,102 1/1909 Brown 75/194 A AND FLOW METER APPARATUSAND FOREIGN PATENTS OR APPLICATIONS METHOD 191,155 7/1967 U.S.S.R 73/194A [75] Inventor: Alvin E. Brown, Redwood, Calif.

Prima Examiner-Charles A. Ruehl 73 A s 1 te 1 1 ss'gnee l g Sys CupemmAttorney-Paul D. Flehr et al.

21 Appl. No.: 268,712

U.S. Cl 73/194 A An ultrasonic speed of sound and flow metering systemwhich may utilize only one pair of ultrasonic [52] transducers byincorporating a unique time share fea- 51 1m. (:1 G01f 1/00, GOlp 5/00in emmdimem a direct Synthesis 8 [58] Field 01 Sflll'ClLm; 73/194 Aquency PmPmional the Speed sound in a Wing medium is obtained using onevoltage controlled oscil- [56] References Cited lator. An additionaldirect synthesis of a data fre- UNITED STATES PATENTS quencyproportional to the flow of the medium is derived from signals inverselyproportional to sound en- 2 ergy transit times upstream and downstream.3,050,997 8ll962 Lake 73/194 A I 21 Claims, 16 Drawing Figures 7 1sTRANS M IT A/ R ECEI V E F LO W D E T E C TO R gee SYNTHESIS CONTROL l9DATA TIME FLOW TOTAL C A L l B DATA FLOW RATE SOUND SPEED 20PATENTEUUEBES I975 VCO sum mar 14 I5 TRANSMIT A/ RECEIVE DETECTOR F i gI I8 r I J SYNTHESIS CONTROL DATA TIME FLOW TOTAL DATA FLOW RATE souNDSPEIED Fig .I3 178 OFF CLOSE 5-6 PATENTEDnmzs I975 3780.577 SHEEI UEOF1A PATENTEDHEE25 I915 3.780.577

sum 07m 14 PATENTEUmes ms 3.780.577

sum as or M zofiowwzo wm W v wwmw mm PATENTEUUEB25 \975 SHEET 10 0F 14ZOCHEE o fl PATENTED UECZS I975 SHEET 13 0F 14 ULTRASONIC FLUID SPEED OFSOUND AND FLOW METER APPARATUS AND METHOD BACKGROUND OF THE INVENTIONThe present invention is directed toward a fluid metering system andmore particularly to a system which provides data indicative of thespeed of sound energy propagation through the flowing medium as well asthe flow characteristics of the medium.

Systems utilizing ultrasonic transducers in communication with a flowingmedium are old in the art. Many systems have been disclosed whichmeasure flow velocity, sound propagation velocity or both. Generallythese systems require a voltage controlled oscillator for each directionof transmission through the flowing medium to provide an upstream anddownstream frequency proportional to the speed of sound. Some systemsemploy switching means whereby one VCO may be made to serve fortransmission in two directions. Other systems impose a quadraturebetween the received signal and the transmitted signal and control theoutput of a VCO through a phase detector. Other methods use the flowingmedium as the frequency determinative element in an oscillating or ringaround system.

Problems commonly arising in the foregoing types of metering systemsrelate to the loss of low flow rate information when using twooscillators, or the requirement for more than one pair of transducerswhen seeking to transmit upstream and down-stream, or the necessity forunwieldy switching means, or any combination of these.

OBJECTS OF THE INVENTION AND SUMMARY It is an object of the presentinvention to provide a measure of the velocity of sound propagationthrough a fluid medium as well as a measure of flow.

It is another object of the present invention to provide a sound speedand flow metering system which utilizes a minimum number of transducers.

It is another object of the present invention to provide a sound speedand fluid flow metering system which in one embodiment synthesizes thesound speed and flow proportional frequencies without using VCOs toprovide frequencies inversely proportional to upstream and downstreamtransmission times.

It is another object of the present invention to provide a sound speedand fluid flow metering system which provides a continuous direction offlow indica tion.

It is another object of the present invention to provide a sound speedand fluid flow metering system which may be utilized for any flowingmedium or pipe or channel size by maintaining a constant phaserelationship between all control and data signals.

It is another object of the present invention to provide a sound speedand fluid flow metering system with fine resolution of measurement downto zero flow.

It is another object of the present invention to provide a sound speedand fluid flow metering system which is bi-directional.

It is another object of the present invention to provide a sound speedand fluid flow metering system with a time calibrated output providingtotal flow and or flow rate.

It is another object of the present invention to provide a sound speedand fluid flow metering system with an accuracy uninhibited byinterference from echoes within the flowing medium caused by priortransmitted pulses.

The foregoing and other objects of the invention are achieved in anultrasonic speed of sound and flow metering system for use in monitoringflow velocity and volume and speed of sound energy propagation throughfluids conveyed in closed conduits or open channels. The system includesmeans for generating signals which are transmitted alternately ingenerally upstream and downstream directions through the fluid and meansfor receiving the signals so transmitted. Means are provided for shapingthe received signal and for generating a reference signal which-is usedfor phase comparison with the shaped received signal. Signal levelsresponsive to the phase relation and proportional to upstream anddownstream sound speeds are generated. The proportional signal levelsare used to generate frequencies proportional to upstream and downstreamsound speeds. Control means are provided which are responsive to theupstream and downstream frequencies to direct the alternatingtransmit/receive feature. Means are provided to combine the upstream anddownstream frequencies to obtain sum and difference frequencies whichare indicative of fluid sound propagation speed and flow respectively.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a simplified block diagram ofthe system.

FIG. 2 is a detailed block diagram of the system including frequencysynthesis.

FIG. 3 is a block diagram of the transmit receive section of the system.

FIG. 4 is a schematic diagram of the transmit receive section of thesystem.

FIG. 5 is a block diagram of the detector section of the system.

' FIG. 6 is a schematic diagram of the detector section of the system.

FIG. 7 is a block diagram of the control section of the system.

FIG. 8 is a schematic diagram of the control section of the system.

FIG. 9 is a block diagram of the frequency synthesis section 'of thesystem.

FIG. 10 is a schematic diagram of the frequency synthesis section of thesystem.

FIG. 11 is a block diagram of the time calibration section of thesystem.

FIG. 12 is a timing chain diagram of the signals in the control sectionof the system.

FIG. 13 is a timing chain diagram of the data fre quency and controlsignals in the frequency synthesis section of the system.

FIG. 14 is a timing chain diagram showing the multiplication of the datafrequency in the frequency synthesis section of the system.

FIG. 15 is a timing chain diagram showing the division of the highfrequency VCO output frequency in the frequency synthesis section of thesystem.

FIG. 16 is a detailed block diagram of a system including voltagecontrolled oscillators for frequency generation.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention described here isa fluid flow metering system which also provides indication of the speedof sound through the flowing medium. The system includes at least onepair of ultrasonic piezoelectric transducers mounted in communicationwith the flowing medium to be measured. One embodiment provides fordirect synthesis of a data frequency proportional to the flow of themedium and of a frequency proportional to the speed of sound in themedium from a single voltage controlled oscillator. The synthesizedsignals are derived from signals proportional to sound energy transittimes through the fluid in generally upstream and downstream directions.The data frequency and oscillator frequency are combined using standardupper and lower side band separation techniques, balanced modulators,and linear frequency mixers. The results are frequencies proportional toupstream and downstream sound speeds through the medium which are usedto control transmission direction, selection of the proper transducerfor reception, and synthesis of the sound speed and flow datafrequencies. As can be seen in FIG.

'1 the system includes a transmit/receive network wherein 'the switchselections are made which provide for alternate functioning of thetransducers as transmitter and receiver and receiver and transmitterrespectively. The received signal is delivered from the transmit/receivenetwork 15 to a detector network 16. The detector network 16 shapes thereceived pulse in a manner disclosed in copending U.S. Pat. applicationSer. No. 250,760. A control network 17 generates a reference pulse whichis directed to the detector network 16. A phase comparison between thereceived pulse and the reference pulse is performed in the detec tornetwork 16 and a signal with its polarity determined by the relativeearly or late nature of the received pulse is directed to the controlnetwork 17. The control network 17 performs summations of the early/latesignals which are delivered to a frequency synthesizing network 18..Thesynthesizing network 18 operating on the summations provides frequencieswhich are proportional to the upstream and downstream sound propagationvelocities. These frequencies are directed to control network 17 toprovide control signals which properly sequence the transmit/receiveswitching performed in the transmit/receive network 15. The controlsignals from control network 17 are also connected to detector network16 providing proper signal sequence for the received signal andreference signal phase comparison, a receiver amplifier automatic gain.control, and a no signal indication alarm. The summations of theearly/late signals from control network 17 are utilized directly withinthe frequency synthesizing network 18 to control the output frequency ofa voltage controlled oscillator 19 and to generate a data frequency. Theoutput of VCO 19 provides a frequency proportional to the speed of soundthrough the flowing medium. The data frequency is proportional to flow.A time calibration circuit 20 receives the data frequency converting itto totalized flow or flow rate as desired on visual indicatorsresponsive to the output from the time calibration circuit 20.

Referring now to FIG. 3 the transmit/receive section 15 of the system isshown in block form. This section of the circuit directs a transmissionpulse to an appropriate transducer and channels the received signal fromthe other transducer to an appropriate amplifier. An up/down input fromthe control circuit 17 is used to generate a pulse from either one shotdevice 21 or 22.

Balance potentiometer 23 is connected to both transmit pulse generators21 and 22 to provide uniform transmit pulse width. The same up/downsignal selects the position of the analog switch 24 which in turnalternately connects first or second receiver amplifier 25 or 26 to thereceived signal conditioning network in the detector 16. Tank circuit 27is provided to boost the received signal from receivers 25 or 26 priorto directing it to the detector circuit 16. Inverter 28 provides thedown signal since onlythe up" signal from control 17 is connected to thetransmit/receive circuit 15. The transmit pulse generators 21 and 22 areconnected to the input of high voltage transmit pulse amplifiers 29 and32 respectively. Transmitter amplifier 29 can be seen to be connected totransducer 33 and transmitter amplifier 32 can be seen to be connectedto transducer 34 in the wall of pipe 35.

Voltage comparator 39 is also alternately connected to the output ofreceiver amplifier 25 or 26 and directs an output to a high-low signallatch circuit 40 which also receives a positive transmit signal fromcontrol section 17. An integrator 41 receives the output of latch 40 anddrives high voltage regulator 44 to meet the amplitude requirements setfor the received signal at the comparator 39. The output of integrator41 is also delivered to a comparator 45 which provides an alarmindication for a predetermined transmit pulse high voltage level whichindicates a low received pulse level and probable malfunction.

Turning now to FIG. 5 a block diagram of the detector section 16 of thesystem is seen. This section of the circuitry receives the signaltransmitted through the flowing medium, conditions it, and makes anearly or late reception decision for the received pulse when comparedwith a reference. Amplifier 46 receives the signal passed on from firstor second receiver amplifier 25 or 26, depending on the setting ofanalog switch 24 in the transmit/receive circuit 15. Automatic gaincontrol 47 adjusts the output of amplifier 46 to a predetermined level.Automatic gain control 47 contains a control comparator 48 and anintegrator 49 which provides an output driving the gain of amplifier 46upward when it is not up to the predetermined level at comparator 48 orreducing it to that level when it exceeds the predetermined level.Comparator 48 is directed to high-low detector 50 which is connected tointegrator gate 51. Gate 51 provides an input to either the inverting ornon-inverting input integrator 49.

The output of amplifier 46 is connected to low level detector 52 whichincludes amplifier 52a. The output of amplifier 52a is directed tocontrol comparator 48 in the AGC loop for amplifier 46. The detector 52amplifier 52a, a differentiator 53, and a comparator 54 are connectedserially and are the major components of the trigger circuit disclosedin copending U.S. Pat. application Ser. No. 250,760.

A cross over comparator 57 also receives the output of amplifier 46 andis connected to a gate 58. A nand gate 59 is connected to set the gate58 and has two inputs. The first input is the trigger signal emanatingfrom comparator 54, and the second is a path to ground applied by areceiver mode switch 60, the position of which determines whethertheoutput from cross over comparator 57 or the output from the triggercircuit comparator 54 is utilized as the received and conditionedsignal. Gate 58 is connected to a charge dispenser 61 and a comparisongate 62. A one shot device 63 delays the reference pulse for the oneshot pulse width and then delivers it to gate 62 through a referencepulse gate 64 for comparison with the received signal from gate 58.

The guard signal from control section 17 is connected to a receivedsignal AGC reset comparator 65. It is also connected to charge dispenser61 and comparator 54 to inhibit those three devices during the dwelltime of the guard pulse. The guard signal is inverted and delivered tothe input of a no signal gate 66 and the charge dispenser 61. Anearly/late gate 67 receives the output from gate 62 and the chargedispenser 61. A pulse at either an early or a late output from gate 67is provided depending on the early or late status respectively of thereceived pulse.

The transmit pulse from control section 17 enables gate 64 as well asthe high-low detector 50 and an additional gate 67. This additional gate68 is reset by a signal from gate 58 and produces an output enabling theno signal" gate 68.

The control section 17 of the system provides generally for thegeneration of the transmit pulse signal, a portion of the delay time andsubsequent generation of the reference pulse, generation of the receiverguard signal, the up/down control signals, and the integrator outputswhich are utilized as control signals in the synthesizer circuit 18.Referring now to FIG. 7 a block diagram is shown for the control section17. Signals are received from the detector section 16 indicating theearly or late status of the received pulse. Latch circuits 69 and 70 arealternately enabled by up/down flip-flop 71 to pass a signal dependingon whether the received signal is early or late. A signal from latchcircuit 69 is connected to either the inverting or noninverting input ofamplifier 72 which provides an input to a first integrator 73. In asimilar manner a signal generated from latch circuit 70 is connected tothe inverting or noninverting input of amplifier 75 which in turnprovides an input to a second integrator 76. Output from bothintegrators 73 and 76 is directed to the synthesizer circuit 18.

Normal operation of the circuit requires continuing changes of state inboth latch circuits 69 and 70 which are monitored by summing and alarmcircuit 77. If either or both latch circuits 69 and 70 cease to changestate for a specified period of time an alarm indication is provided byalarm circuit 77.

The control section 17 also receives two-frequencies from thesynthesizer 18 which are directed to switching circuit 78 which performsa single pole/double throw function. Switching circuit 78 also receivesinputs from the up down control flip flop 71. The up" signal fromup/down 71 is also directed to the transmit/receive circuit for controlof analog switch 24.

Switching circuit 78 is connected to transmit pulse generator 82 andalso to divider circuit 83. Divider circuit 83 is connected to referencepulse generator 84 and to a pulse generator 87. Pulse generator 87 is inturn connected to guard pulse generator 88 which affords a guard signaland an input to the up/down control 71. Receiver guard 88 also providesone input to a gate 89 which is connected to a repetition rate pulsegenerator 90. Pulse generator 90 is connected to enable the transmitpulse generator 82.

A signal from receiver guard 88 is connected to the detector section 16and the signal from the reference pulse generator 84 is delivered toboth the detector section 16 and transmit/receive section 15. The twosignals from the transmit pulse generator are of opposite polarity. Thelow transmit pulse is connected to the detector circuit 16 and the hightransmit pulse is delivered to the transmit/receive circuit 15.

Referring now to FIG. 9 a block diagram of the frequency synthesizersection 18 of the system is seen. In accordance with well known upperand lower sideband separation techniques, balanced modulation, andlinear frequency mixer utilization, frequencies are synthesizedproportional to upstream and downstream propagation velocities. Firstand second integrators 73 and 76 from control circuit 17 are againdepicted. The integrators 73 and 76 are seen to be connected to asumming circuit 93 which provides a mean value of the two integratoroutputs to an integrator 94. Integrator 94 functions as the controlsignal generator for the high frequency VCO l9. Divider circuit 96receives the output of high frequency VCO 19 and generates two signalsin quadrature at one quarter of the frequency of the oscillator 19.These square wave signals, which may be referred to as sine theta andcosine theta are delivered to balanced modulators 99 and 100respectively.

The signals from the first and second integrators 73 and 76 are alsodelivered through switches 101 to fast integrators 102 and 103. Theoutput of integrators 102 and 103 are directed to modulators 99 and 100respectively. The output signals from modulators 99 and 100 are balancedby potentiometers 105 and 106 respectively. v The outputs from the fastintegrators 102 and 103 are also delivered to comparators 107 and 108which provide a square wave output at the output frequency and therelative phase of the fast integrators 102 and 103. The outputs fromcomparators 107 and 108 are utilized to actuate switch controls 110 and111 respectively. Switches 101 are positioned by virtue of such controlto provide trapezoidal wave forms in quadrature at the outputs of fastintegrators 102 and 103 which may be referred to as sine (b and cosinedz respectively.

The balanced modulated output signals from modulators 99 and 100 areconnected to linear frequency mixers 112 which are in turn connected inpredetermined combinations to low pass filtering circuits 113 and 114.The frequency outputs from filters 113 and 114 are proportional toupstream and downstream sound propagation velocities respectively aswill be shown in the functional description which follows. These twofrequencies are delivered to control circuit 17 as synthesized outputsfrom first and second voltage controlled oscillators.

The outputs of comparators 107 and 108 are connected to a flow directionphase detection gate 117 which in turn provides an input to an exclusiveOR gate 1 18. Gate 118 provides an output indicative of flow direction.The outputs from comparators 107 and 108 are also directed to amultiplier circuit 119 which provides an output at four times thecomparator output frequency. A one shot device 120 receives the outputfrom multiplier 119 and provides a data frequency output having aconstant charge in each data pulse.

The data frequency from one shot device 120 is proportional to flow asmentioned before. Several means by which the data frequency may bereduced to readable form are displayed in FIG. 11. First there is thewell known method and circuitry provided in a digital to analogconverter 123. Second the data frequency pulses by design present aconstant charge per pulse so that they may be used to drive a frequencyto analog converter 124. Such a frequency to analog device might takethe form of a DArsonval meter movement with a mechanical action urged bythe data frequency pulses which are filtered or smoothed by the inertiaof the mechanical action in the meter. A third means of reducing thedata frequency is through the injection of time calibration.

FIG. 11 shows a read only memory 125 which has a program patch and whichis connected to an adder 126. The adder 126 is connected to one of theinputs of a latch 129. Latch 129 also receives the data frequency fromthe one shot device 120. The output of the adder 126 is transferredthrough the latch 129 to an accumulator 130 by a data frequency pulse.The output of the accumulator 130 is directed back to the adder 126.

Upon accumulation .of a predetermined number of pulses the accumulator130 generates a carry pulse which may be sent to circuitry which willeither provide flow rate information or total flow information. In thetype of circuit providing flow rate information the carry pulse isdirected to an'up-down counter 131. An input from a clock 132 isconnected to the up-down counter 131. A borrow and a carry output areconnected from the up-down counter 131 to a flow rate display 135. Theborrow output is connected to the input of a flip flop device 136.Outputs from the flip flop 136 are directed to the flow rate display 135and to an exclusive OR gate 137. Another input to the OR gate 137 isprovided by the output of the exclusive OR gate 118 in FIG. 9. Theoutput of gate 137 is directed to the counter 131 to direct the counterto count up or down.

Should the flow information be desired in terms of totalized flow thecarry pulses from the accumulator 130 are directed to a second up-downcounter 138. A total flow display 141, a flip-flop 142 and an exclusiveOR gate 143 are connected in a manner identical to that described forthe flow rate display above. A reset function is provided in'the secondcounter 138 to provide for clearing prior counts to beging a new total.

Referring to FIG. 2 there is seen a detailed block diagram of the entiresystem and the interconnections between the major sections.

We turn now to the operation of the system just described. ln the mostgeneral sense a transmit signal is generated, transmitted upstream ofthe flow, received, conditioned and used to trigger a transmit signalwhich is transmitted downstream of the flow. This process is repeated,transmitting alternately upstream and downstream. ln this fashionupstream and downstream transmission repetition rates arise proportionalto frequencies hereinafter referred to as upstream and downstreamfrequencies. Referring to FIG. 3 the generation and reception of atransmitted pulse will be discussed. Assuming that the up-down controlfrom control section 17 selects transmitter one shot device 21,. asquare positive going pulse is applied to the input of transmitteramplifier 29. A negative going pulse from the high voltage regulatedsupply 44 is directed to the upstream situated transducer 33 in the pipewall 35. Diodes D1 and D2, seen in FIG. 4, perform an important receivernoise isolation function. In the circuit being described they have a 0.7volt junction potential which must be overcome prior to conduction. Allnoise from power supply 44 and the remainder of the transmittercircuitry is below 0.7 volts.

Energy transferred to the flowing medium is received by the down streamtransducer 34 and delivered to the input of receiver amplifier 25. Thesame up control pulse which selected transmitter one shot 21 alsodirects the analog switch control 24 to close the switch at the outputof receiver amplifier 25 while maintaining the switch at the output ofreceiver amplifier 26 in the open condition. Thus the received pulsefrom amplifier 25 is delivered to the tank circuit 27 which is tuned tothe received pulse frequency. A gain in received pulse amplitude isobtained through resonance in the tank circuit 27 which also suppressesundesired frequency components in the received pulse in the manner of aband pass filter. The received pulse is then directed to receiver 46 inthe detector section 16.

The received signal is also directed from tank circuit 27 to a receivedpulse amplitude detector 39 which is a voltage comparator. Thecomparator 39 is connected to the high-low signal latch 40 whichcontrols the integrator 41. The integrator 41 controls the output levelof high voltage regulator 44 which provides the high voltage transmitpulses. This provides an AGC loop wherein a constant received pulseheight is maintained by adjusting the transmitted pulse height.

The output of integrator 41 also works into a comparator 45 whichproduces an output when the transmitted pulse reaches a predeterminedhigh level. The output of comparator 45 actuates an alarm because a hightransmitted pulse level is produced through the AGC loop by a lowreceived pulse level indicating probable malfunction in the system. forhigher Having transmitted a pulse in a down-stream direction the up-downcontrol from control section 17 now selects transmit one shot 22 toprovide an input to transmitter amplifier 32which in turn produces anegative going high voltage transmit pulse to transducer 34. The energyis transmitted in a relatively upstream direction and received bytransducer 33. The received signal is delivered to receiver amplifier 26and through the switch at the output of amplifier 26 which is closed bythe same signal which selected transmit one shot 22 to produce thetransmit signal. The remainder of the transmit receive circuit functionsidentically whether transducer 33 or transducer 34 functions as thereceiver.

Turning now to the detector section 16 reference is made to FIG. 5. Thereceived signal from the transmit receive section 15 is presented at theinput to the amplifier 46. The received signal is conditioned andpresented to gate 58 as disclosed in copending US. Pat. application Ser.No. 250,760. The receiver mode switch 60 provides a low input to nandgate 59 when it is closed to ground. Gate 59 presents a continuous upstate so the set input of gate 58 under this condition. The output fromcomparator 54 resets gate 58 and the next pulse from cross-overcomparator 57 tires gate 58. in the case of flowing media injecting toomuch phase noise in the output of cross-over comparator 57 the receivermode switch 60 is opened. This places a high state on one input of thenand gate 59 which allows a low output to be sent to the set input ofgate 58 each time comparator 54 produces a pulse. The pulse fromcomparator 54 connected to the reset of gate 58 initiates the output ofgate 58 directly in this instance.

The output of gate 58 represents the time of arrival of the receivedpulse and is delivered to gate 62 for comparison with the time ofarrival of the reference justed to match the delay imposed on thereceived pulse as disclosed in copending US. Pat. application Ser. No.250,760. The received pulse from gate 58 is also connected to chargedispenser 61. The charge dispenser produces a pulse with a widthextending from the end of the received pulse to the beginning of thenext guard pulse from control section 17. The early/- late gate 67contains a'pair of nor gates which receive the outputs from thecomparison gate 62 and the charge dispenser 61 and provide a signal ateither an early or a late output terminal. The inputs to gate 67 areconnected so that a downgoing signal appears at the early output if thereceived signal arrives at the comparison gate 62 prior to the referencepulse from gate 64. Conversely a down going signal appears at the lateoutput of gate 67 if the received pulse is later than the referencepulse.

The low transmit pulse is also used to reset the additional gate 68which is then fired by the output from gate 58. The high output state ofgate 68 is connected to the no signal gate 66. One output from the nosignal gate 66 is held in a down state by the signal from gate 68. Theinverted guard pulse holds the same output from gate 66 down while thegate 68 is being reset. A continuous down output from gate 66 is anindication of normal received signal operation and conversely an upoutput from gate 66 indicates a probable malfunction since receivedsignal outputs are not being produced from gate 58.

The low transmit pulse also resets the high-low detector 50. The outputsfrom detector amplifier 52a is connected to the AGC control comparator48 and the AGC reset comparator 65. The output of control comparator 48is connected to the high/low detector 50. The reference voltage at thecontrol comparator 48 is less than that at the reset comparator 65. Whenthe output from the detector amplifier 52a is higher than the referenceset in control comparator 48 it produces a signal directed to thehigh/low detector 50. The high/- low detector 50 output is sent tointegrator gate 51. The output from gate 51 is connected to the input ofintegrator 49 which results in a gain control signal from integrator 49which decreases the gain of amplifier 46. When the output from detectoramplifier 52a exceeds the reference set in reset comparator 65 an outputis produced which when delivered to the integrator gate 51 generates anoutput from gate 51 which continuously drives integrator 49 in adirection to reduce the gain of amplifier 46. This latter feature is abackup for the control comparator function. Integrator gate 51 is set tourge amplifier 46 to a high gain condition until directed otherwise bycontrol comparator 48 or reset comparator 65.

Turning now to the operation of the control section 17 of the systemreference is made to FIG. 7. Latches 69 and 70 each contain two pair ofnor gates. An early or a late signal arriving from the detector section16 is in the form of a down going pulse. Thus an up indication fromup/down control 71, which is in fact a low state, enables the first pairof nor gates in latch 69 while the simultaneous high state signal fromup/down control 71 to latch blocks the first pair of nor gates containedtherein. Latch 69 is now in a condition to conduct either an early or alate pulse to amplifier 72. An early pulse is directed to theinvertinginput of amplifier 72, and a late pulse is directed to the non-invertinginput. The resulting output from amplifier 72 is directed to theinverting input of integrator 73 causing the integrator output voltageto rise in the case of an early received pulse and to fall in the caseof a late received pulse.

The outputs from the first pair of nor gates contained in latch 69 arealso delivered to a second pair of contained nor gates in such a manneras to cause their output states to change each time a transition is madebetween an early and a late pulse through the latch 69. Latch 70functions in a manner similar to latch 69, sending an early or a latepulse to the inverting or noninverting input respectively of amplifier75 which in turn produces an output driving integrator 76 in the samefashion as described for integrator 73 above. Latch 70 also produces aconstantly changing state from a contained second set of nor gates ifthere is a constant transition between early and late pulses passingthrough to integrator 76. The changing states from latches 69 and 70 asa result of early/late transition are both directed to a summing andalarm circuit 77. Alarm circuit 77 contains a retriggerable one shotdevice which holds an alarm indication in a constantly up state as longas both latches 69 and 70 produce changes in state within the one shotperiod of the retriggerable device. In the event either latch 69 or 70fails to display changes of state within such period, the alarm outputfalls to a low state indicating malfunction in the system.

Referring nowto FIG. 12 there is pictured a timing chain for a portionof the control section 17. A clock frequency 144 is shown as arelatively high frequency and is the synthesized frequency f, or f whichis generated in the synthesizer section 18 and connected to the switchcircuit 78. Switch circuit 78 passes either f, or f depending upon thestate of the up/down control 71. For example when the up/down control 71is in the up selection condition it passes f, through the switch circuit78 and blocks f f, is delivered to the clock input of the divider 83. Arepetition rate pulse 147 is generated by the divider circuit 83 whichhas a period of 128 clock pulses. A second divider output pulse 148rises at the end of 128 clock pulses and falls at the end of 256 clockpulses. The second divider output 148 is connected to the guard andup/down initiate pulse generator 87. Pulse generator 87 fires on therise of divider output 148 and terminates on the subsequent rise of onthe fall of pulse 149. Pulse 150 is delivered to one input of gate 89.The second divider output pulse 148 is delivered to the reference pulsegenerator 84 and generates a pair of outputs 154 and 155 on the fall ofthe pulse 148. Pulse 154 is directed to the transmit receive section 15to allow comparator 39 to function during its dwell time and to enablethe high-low signal latch 40. Pulse 154 is also connected to detectorsection 16 where it is processed and compared in time phase with theprocessed received pulse. Pulse 155 from the reference pulse generator84is directed to the second input of gate 89. Pulsel50 returns to a lowstate

1. In an ultrasonic speed of sound and flow meter system of the typeutilizing first and second transducers spaced in relativeupstream-downstream positions in communication with the fluid to bemetered, means for generating signals to be transmitted by saidtransducers through said fluid, means for receiving signals sensed bysaid transducers, means for generating a reference signal, means forcomparing the phase of the received signal and the reference signal andgenerating a phase dependent signal, means responsive to said phasedEpendent signal for generating signal levels proportional to upstreamand downstream speeds of sound, means responsive to said signal levelsfor providing frequencies proportional to upstream and downstream speedsof sound, control means utilizing said frequencies for directingtransmission alternately by said first and second transducer andreception alternately by said second and first transducer respectively,and means combining said frequencies whereby a sum frequency is obtainedproportional to the speed of sound in the medium and a differencefrequency is obtained proportional to the flow rate of the medium.
 2. Anultrasonic speed of sound and flow meter system as in claim 1 whereinthe means providing frequencies proportional to upstream and downstreamspeeds of sound comprise first and second voltage controlled oscillatorsreceiving downstream and upstream transmitted signals respectively andwherein said means combining said frequencies comprise a balancedmodulator, said modulator operating to provide said sum frequencyproportional to speed of sound in the medium and said differencefrequency indicative of flow rate.
 3. An ultrasonic speed of sound andflow meter system as in claim 1 wherein said means providing frequenciesproportional to upstream and downstream speeds of sound and said meanscombining said frequencies comprise a voltage controlled oscillator,means for controlling the output frequency of the voltage controlledoscillator utilizing said speed of sound proportional signal levels toprovide said frequency indicative of sound propagation speed through themedium, means for synthesizing a data frequency utilizing said speed ofsound proportional signals to provide said frequency indicative of flowrate, and means combining said oscillator and data frequencies.
 4. Anultrasonic speed of sound and flow meter system as in claim 3 togetherwith transmit signal automatic gain control responsive to the amplitudeof said received signal, and voltage comparator means responsive to apredetermined amplitude transmit signal indicating a low received signaloperating to generate an alarm and to block data from said oscillatorand data frequencies.
 5. An ultrasonic speed of sound and flow metersystem as in claim 3 wherein said means for controlling the outputfrequency of said voltage controlled oscillator comprises a summingcircuit receiving said signal levels proportional to upstream anddownstream speeds of sound, an integrator responsive to the output ofthe summing circuit, said integrator operating into said voltagecontrolled oscillator whereby a change is effected at said oscillatoroutput proportional to the integral of said summing circuit output. 6.An ultrasonic speed of sound and flow meter system as in claim 3 whereinsaid means for synthesizing a data frequency utilizing said speed ofsound proportional signals comprises first and second integratorcircuits to receive said upstream and downstream speed of soundproportional signals, first and second comparators to receive theoutputs of said first and second integrators respectively, switchingmeans to direct the upstream frequency proportional signal alternatelyto said first and second integrators and actuated by said secondcomparator, switching means to direct said downstream frequencyproportional signal alternately to said first and second integrators andactuated by the output of said first comparator, and a frequencymultiplier circuit to receive the outputs of said first and secondcomparators to provide a frequency indicative of flow.
 7. An ultrasonicspeed of sound and flow meter system as in claim 6 together with abi-directional flow indication actuated by phase relationship betweensaid first and second comparators.
 8. An ultrasonic speed of sound andflow meter system as in claim 3 wherein said means combining saidoscillator and data frequencies comprises a frequency divider to receivethe output of said voltage controlled oscillator, a pair of outputsignals in quadrature from said frequency divider, first and secondbalanced modulators, a pair of outputs in quadrature from said means forsynthesizing a data frequency, circuit means directing said leadingdivider frequency and said lagging data frequency to said first balancedmodulator, circuit means directing said lagging divider frequency andsaid leading data frequency to said second balanced modulator, linearfrequency mixing means to receive the outputs of said first and secondbalanced modulators, said mixing means operating to provide first andsecond frequency outputs proportional to downstream and upstream speedsof sound respectively.
 9. An ultrasonic speed of sound and flow metersystem as in claim 1 wherein said control means utilizing saidfrequencies for directing transmission alternately by said first andsecond transducers and reception alternately by said second and firsttransducers respectively comprises circuit means responsive to apredetermined number of cycles of said upstream and downstreamfrequencies providing an up/down control, first switching meanssensitive to said up/down control to alternately direct said signals tobe transmitted to said first and second transducers, second and firstpreamplifiers receiving said signals sensed by said second and firsttransducers respectively, second switching means sensitive to saidup/down control to direct output alternately from said second and firstpreamplifiers, a trigger circuit to define the phase of said receivedsignal, said trigger circuit output directed to said means for comparingthe phase of the received signal and the reference signal.
 10. Anultrasonic speed of sound and flow meter system as in claim 1 whereinsaid means for comparing the phase of the received signal and thereference signal and generating a phase dependent signal comprisescircuitry having first and second output and providing one of said firstand second outputs dependent on phase lead or lag of said receivedsignal relative to said referer signal and wherein said means responsiveto said phase dependent signal for generating signal levels proportionalto upstream and downstream speeds of sound comprises circuitry forproviding a signal level having a polarity determined by said one ofsaid first and second outputs for both upstream and downstreamtransmissions and for integration of said signal level having a polarityseparately for both upstream and downstream transmissions.
 11. Anultrasonic speed of sound and flow meter system as in claim 1 whereinsaid means for generating signals to be transmitted by said transducersand said means for receiving the signals sensed by said transducerscomprise switching means for directing said transmission signals to saidfirst transducer, circuit means for receiving and shaping a signaltransmitted generally downstream, circuit means directing said shapedsignal to actuate said switching means directing the subsequent transmitpulse to said second transducer for transmission generally upstream. 12.An ultrasonic speed of sound and flow meter system as in claim 1together with an alarm indication providing evidence of loss of systemtracking when said means for comparing the phase of the received signaland the reference signal does not display a reversal within a presetperiod of time to said means responsive to said phase dependent signal.13. An ultrasonic speed of sound and flow meter system as in claim 1together with a preset repetition rate proportional to upstream anddownstream speeds of sound, said repetition rate providing suppressionof echoes generated within the flowing medium by prior transmissionpulses.
 14. In an ultrasonic speed of sound and flow meter system of thetype utilizing first and second transducers spaced in relativeupstream - downstream positions in communication with the fluid to bemetered, means for alternately transmitting signals through the fluidfrom said first and second transducers respectively, means for receivingsignals from thE fluid in said second and first transducersrespectively, means for generating a reference signal, means forcomparing said reference signal with said received signals andgenerating a comparison signal, means responsive to said comparisonsignal for generating signals proportional to upstream and downstreamtransmission times, and means responsive to said last named signals forsynthesizing frequencies proportional to said upstream and downstreamtransmission times, said synthesizing means forming a sum frequency anda difference frequency of said upstream and downstream transmissionfrequencies indicative of fluid sound propagation velocity and flow raterespectively.
 15. In an ultrasonic speed of sound and flow meter systemof the type utilizing first and second transducers spaced in relativeupstream/downstream positions in communication with the fluid to bemetered, means for alternately transmitting signals to the fluid fromsaid first and second transducers respectively, means for receivingsignals from the fluid in said second and first transducersrespectively, means for generating a reference signal, and meansresponsive to said received and reference signals for generatingfrequencies proportional to the upstream and downstream speeds of sound,said frequencies combining to form a sum frequency indicative of soundpropagation velocity through the fluid and a difference frequencyindicative of flow rate.
 16. A method of measuring fluid flow rate andvelocity of sound propagation through a flowing fluid utilizing at leastone pair of first and second ultrasonic energy transducers capable offunctioning as transmitters and receivers in communication with thefluid which comprises generating a transmit pulse, transmitting saidtransmit pulse from said first transducer through said fluid in agenerally downstream direction, generating a reference pulse, receivingsaid transmitted pulse at said second transducer, comparing the receivedpulse and the reference pulse in phase and generating a signal withphase dependent polarity, connecting said signal with phase dependentpolarity to a first summing network, generating a first control signalin said first summing network, alternating the direction of thesubsequent transmit pulse to said second transducer with said firstcontrol signal, transmitting a subsequent transmit pulse from saidsecond transducer through said fluid in a generally upstream direction,generating a subsequent reference pulse, receiving said subsequenttransmit pulse at said first transducer, comparing the subsequentreceived pulse and the subsequent reference pulse in phase andgenerating a subsequent signal with phase dependent polarity, connectingsaid subsequent signal with phase dependent polarity to a second summingnetwork, generating a second control signal in said second summingnetwork, controlling the output of a high frequency VCO with the meanvalue of said first and second control signals, synthesizing a datafrequency responsive to said control signals, said VCO and datafrequencies providing a signal frequency proportional to the speed ofsound through the medium, and a signal frequency proportional to flowrate respectively.
 17. A method of measuring fluid flow rate andvelocity of sound propagation through the fluid utilizing at least onepair of first and second ultrasonic energy transducers capable offunctioning as transmitters and receivers in communication with thefluid which comprises generating a transmit pulse, generating areference pulse, directing the transmit pulse alternately upstream anddownstream of the flowing medium, receiving the transmit pulse,comparing phase of the received and reference pulses, generating asignal dependent on said phase comparison, generating signalsproportional to upstream and downstream sound speeds responsive to saidsignal dependent on phase, summing said proportional signals,controlling a voltage controlled oscillator with said sum, generating adata frequency utilizing Said proportional signals, combining said datafrequency with said oscillator frequency to synthesize upstream anddownstream sound speed frequencies, generating control signalsresponsive to said sound speed frequencies, said control signalsoperating to maintain a constant time relation between all systemsignals for varying fluid characteristics and different size flowconduits.
 18. A method of measuring fluid flow rate and velocity ofpropagation as in claim 17 wherein generating a signal dependent on saidphase comparison and generating signals proportional to upstream anddownstream sound speeds comprises directing downstream received signalsto a first channel, directing upstream received signals to a secondchannel, generating a pulse of one polarity for received pulse phaseleading reference pulse and of opposite polarity for reference pulsephase leading received pulse, delivering said pulses in said firstchannel to a first integrator, delivering said pulses in said secondchannel to a second integrator, said integrators operating to sum pulsesand to provide outputs proportional to downstream and upstream soundspeeds respectively.
 19. A method of measuring fluid flow rate andvelocity of sound propagation as in claim 17 wherein generating a datafrequency utilizing said proportional signals comprises directing saidsignals to first and second fast integrators, connecting said first andsecond integrators to first and second voltage comparators, directingthe output of said first voltage comparator to alternately switch theupstream and downstream proportional signals to the input of said secondfast integrator, directing the output of said second comparator toalternately switch the upstream and downstream proportional signals tothe input of said first fast integrator, and combining said first andsecond comparator outputs.
 20. A method of measuring fluid flow rate andvelocity of sound propagation as in claim 19 wherein combining saidfirst and second comparator outputs comprises multiplying the frequencyat said first and second comparator outputs to provide a data frequency,and providing a constant data frequency pulse charge to facilitate datareduction.
 21. A method of measuring fluid flow rate and velocity ofsound propagation as in claim 17 wherein combining said data frequencywith said oscillator frequency comprises dividing said oscillatorfrequency to obtain two outputs in quadrature, directing said datafrequency and said divided oscillator frequency to first and secondbalanced modulators, mixing the outputs of said first and secondmodulators to obtain a sum frequency and a difference frequency of theoscillator and data frequencies whereby the balanced modulator outputfrequencies are proportional to upstream and downstream speeds of sound.